So sorry for your loss. If you still have her body, place it in a plastic bag and refrigerate it. In the morning, contact your state vet or poultry lab for a necropsy to look for a cause of death. Here is some contact info for most state vets:
http://www.metzerfarms.com/PoultryLabs.cfm
It sounds and looks like possible Mareks disease. But riboflavin deficiency can also cause walking or sitting on hocks, curled under toes, and lameness. I have a bird right now who I am trying to determine if she has Mareks. She started limping and losing balance, using her wings to get around...